Measuring water content of heavy petroleum fuel oils by infrared analysis



fl- 9, 1969 R. A. SAUNDERS 3,462,596

MEASURING WATER CONTENT OF' HEAVY PETROLEUM FUEL OILS BY INFRARED ANALYSIS Filed Dec. 1. 1967 m SOURCE DETECTOR AMP ATTORNEYS United States Patent 3,462,596 MEASURING WATER CONTENT OF HEAVY P E- TROLEUM FUEL OILS BY INFRARED ANALYSIS Raymond A. Saunders, 5113 72nd Ave., Hyattsville, Md. 20784 Filed Dec. 1, 1967, Ser. No. 687,334 Int. Cl. G01n 21/26 US. Cl. 250--43.5 7 Claims ABSTRACT OF THE DISCLOSURE A method and apparatus for measuring the water content of heavy petroleum fuel oils using infrared analysis. Heavy fuel oil, in transit in a supply line, is sampled and delivered in continuous manner into a confined low pressure zone in which the water content of the sample fuel oil is flash vaporized and the water vapor dra'wn across a beam of periodically interrupted infrared radiation containing wavelengths of radiation at which water vapor characteristically absorbs. The absorption of the radiation is measured and related to the water content of the fuel oil. The apparatus includes a light beam chopper, a tubular low pressure sample cell, an infrared radiation detector, an amplifier and a recorder. The sample cell has filter windows mounted in the upper end for transmission of a beam of periodically interrupted infrared radiation and a heater element in the lower end for raising the temperature of the incoming sample fuel oil. A feed line and a return line connect the sample cell to the fuel oil supply line, with the feed line arranged to deposit the fuel oil sample on the heater element.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to a method and apparatu for measuring the water content of heavy petroleum fuel oils, more particularly for continuously monitoring the water content of heavy petroleum fuel oils which are in transit to marine boilers.

BACKGROUND OF THE INVENTION Slagging of boiler tubes is a continuing problem in the operation of marine boilers. The slagging lowers the heat transfer rate and thereby the operating efliciency of the boilers. Slag is an extremely hard, difficult to remove, material which results from the fusion on boiler tubes of accumulated deposits of inorganic products from the combustion of heavy petroleum fuel oils. A major factor in the development of slag is the presence of salt water in the fuel oils. As little as 0.5% by weight saltwater in the fuel oil will materially increase the rate of deposition of solids on the boiler tubes. The use of sea water ballast is the major source of salt water contamination of the fuel oils. The content of sea water in the heavy fuel oils will vary over a rather wide range, from about 1 to 40% by weight, with a general average content being about 2 to 3% by weight. Occasionally the fuel oil will contain a slug of water of sufiicient size to actually extinguish the boiler flame. Measurement of the water content of the heavy fuel oils is, therefore, of prime importance in the efficient operation of marine boilers.

Itis an object of the present invention to provide a method of quickly measuring the water content of heavy petroleum fuel oils.

It is also an object to provide a method of continuously monitoring the water content of heavy petroleum fuel oils which are in transit to marine boilers.

it is a further object to provide an apparatus for Patented Aug. 19, 1969 "Ice quickly measuring the water content of heavy petroleum fuel oils using an infrared analyzer.

STATEMENT OF INVENTION The above and other objects are accomplished by the present invention in which heavy petroleum fuel oil in transit in a supply line is sampled and delivered in continuous manner into a confined low pressure zone in which the water content of the sample fuel oil is flash vaporized and the water vapor drawn across a beam of periodically interrupted infrared radiation containing Wavelengths of radiation at which water vapor characteristically absorbs. The absorption of the radiation is measured and related to the water content of the fuel oil. A suitable beam of infrared radiation for measurement of the water content of the fuel oil is one defining an optical interval of approximately 1.8-9 microns or a narrower interval of approximately 46.5 microns.

The invention is intended primarly for measurement of the Water content of heavy petroleum fuel oils which contain less than about 10% by weight water, although it may also be applied for the measurement of water content in cases where the fuel oils contain greater amounts of water, up to about 40% by weight.

The term heavy petroleum fuel oil is used herein in the customary sense in the art to designate high boiling point residual petroleum fuel oils, such as bunker or grade No. 4, S and 6 fuel oils, and high boiling point residual petroleum fuel oils which have been cut back in viscosity by blending with a lighter petroleum fuel oil known as cutter or cycle stock and the resulting blended heavy fuel oil has a flash point minimum of F. (closed cup). Cutter or cycle stock are fractions slightly heavier than kerosene. Examples of such blended heavy fuel oils are those known under the appellation of Navy Special Fuel Oil, a specific example of which is a blend of grade No. 6 or bunker C fuel oil with cycle stock to give a blended heavy fuel oil of 22.1 seconds Saybolt Furol at 122 R, an AP I gravity at 60 F. of 20.7, and a flash point of F. (closed cup).

The invention will be more fully understood from the following description when read in conjunction with the accompanying drawing in which the single figure is a schematic showing, partly in section, of an apparatus for practicing the invention.

Referring to the drawing, a tubular steel cell 10 having detachable conical-shaped ends 34 and 35 is connected to the heavy fuel oil supply line 11 by a feed line 12 for delivery of sample fuel oil to the cell and by a return line 21 for return flow of water-stripped sample fuel oil from the cell to the supply line. The cell 10 may have an inner diameter of from about 1 to 10 inches and is constructed to be operated at low pressures, e.g., about 0.1-5 mm. Hg.

The feed line 12 has an upturned terminal portion 13 within the fuel oil supply line 11 for pickup of sample fuel Oil and a downturned terminal portion 17 within the cell 10 for delivery of the sample fuel oil to the cell. A threeway valve 14 and a metering pump 15 are provided in the feed line 12 for control of flow of sample fuel oil from the supply line to the cell 10. A preheater 16 envelops the feed line 12 near the sample cell 10 and may be of conventional construction with electrical resistance coils arranged around the feed line.

A heater element 18 is mounted and arranged in the lower portion of the cell 10 to receive sample fuel oil thereon from the downturned outlet 17 of the feed line 12. This heater element may be a conventional, electrically heated hotplate having the resistance coils enclosed within the plate. The hotplate is connected to a conventional temperature control means (not shown) which includes a rheostat located outside the cell 10.

The return flow line 21 is connected to the lower conical-shaped end 35 of the sample cell and has a downturned terminal outlet 22 within the fuel oil supply line 11. A pump in the line 21 assists delivery of waterstripped sample fuel oil from the sample cell to the fuel oil supply line.

A low pressure line from an exhausting device, such as a vacuum pump 31, is connected to the sample cell 10 at the upper conical-shaped end 34. A manometer 32 may be used in the line 30 for controlling the low pressure in the cell 10. If desired, the manometer may be used in conjunction with a controlled air leak (not shown) located in the wall of the cell 10 near the sample inflow outlet 17 or in the feed line 12 between the metering pump 15 and the preheater 16. A discharge line 33 is connected to the vacuum pump 31 for delivery of vapors from the cell 10 to the firebox of the boiler.

Inclined steel baffles 19 are arranged in and attached to the wall of the sample cell 10 to hold back gross or liquid particles of fuel oil from passing into the path of the beam of infrared radiation in the upper portion of the cell.

An infrared source 23 and a light beam chopper 24 are arranged to deliver a beam of periodically interrupted infrared radiation to the entrance filter window 25 which is mounted in the wall of the cell 10 along with the exit filter window 26. These filter windows are selected to be water-resistant and to define a pass band of the chopped infrared radiation which is appropriate for measuring the water content of the fuel oil. The infrared radiation transmitted by the filter window 26 is picked up by an infrared radiation detector 27 which is electrically connected to an amplifier 28 of matching frequency and to a recorder 29. The detector 27 may be a bolometer and the recorder 29 may be a strip chart recorder or a panel meter.

For a band pass of the infrared radiation in the region of approximately 1.8-9 microns, the entrance filter window 25 may be germanium which has a lower light transmission limit at approximately 1.8 microns and the exit filter window 26 may be lithium fluoride which has an upper light transmission limit at approximately 9 microns. For the narrower band pass of approximately 4-6.5 microns, the filter window 25 may be indium arsenide which alloyed with indium antimonide to have a lower light transmission limit at approximately 4 microns and the filter window 26 may be sapphire which has an upper light transmission limit at approximately 6.5 microns. The thickness of filter windows 25 and 26 may be about one centimeter or less depending on the strength of the window material in respect to the low pressure in the cell 10.

Water vapor characteristically absorbs infrared radiation at approximately 2.5-3 microns and 5.5-7 microns. Hydrocarbon vapors characteristically absorb infrared red radiation at approximately 3.3-3.5 microns, 6.7-6.75 microns and 7.2-7.3 microns.

The optical distances between the filter Windows 25 and 26 may vary and by the use of multiple reflectance optics, as is known in the art, range up to, for example, the equivalent of 10 meters actual. Longer optical paths, actual or equivalent, between the filter windows are used when the water content of the heavy fuel oils under test is known or suspected to be relatively low, e.g., 0.5% by weight and less, to provide, in effect, a longer absorption path for the water vapor.

In the practice of the invention for continuous monitoring of the water content of a heavy petroleum fuel oil in transit in the supply line from the bunker to the boiler aboard ship, the valve 14 in the feed line 12 is opened for flow of the sample fuel oil from the fuel supply line 11 to the sample cell 10 operating at low pressure. The rate of flow of the fuel oil to the cell 10 is matched to that of the heavy fuel oil in the supply line 11 and governed by operation of the measuring pump 15. The volume of the sample fuel oil delivered per unit of time to the cell 10 may be, for example, from about to 100 cc. per second and is governed by the cross-section of the feed line 12. The inner diameter of the line 12 is suitably from about to inch.

The heavy fuel oil in transit in the supply line 11 aboard ship is in a heated condition, usually at a temperature of about F. for Navy Special Fuel Oil. The sample fuel oil in flowing from the supply line to the sample cell by way of the pickup 13 and feed line 12 is further heated, to a temperature of about 200 F., by operation of the preheater 16, before being delivered by the outlet 17 onto the heater element 18 where it is again further heated to a temperature of, for example, about 225250 F., to ensure flash evaporation of the total water content of the sample fuel oil under the prevailing low pressure in the cell 10. This low pressure may be, for example, of the order of from about 0.1-5 mm. Hg. The heater element 18 should be operated at temperatures as low as possible consistent with effecting the desired rise in temperature of the incoming sample heavy fuel oil to the end of incurring a minimum of sludging of the fuel oil.

Where Navy Special Fuel Oil is monitored for water content the vaporized water and concomitantly vaporized light hydrocarbons from the sample fuel oil are drawn by the pull of the operating vacuum pump 31 across a periodically interrupted beam of infrared radiation which is chopped at a predetermined frequency, for example, at 13 c.p.S., by the light chopper 24 and contains wavelengths of infrared at which water vapor and hydrocarbon vapors absorb. A filter window 25 of germanium and a filter window 26 of lithium fluoride define a band pass of the infrared radiation which extends over the interval of approximately 1.8-9 microns. The beam of infrared radiation transmitted by the exit filter window 26 falls on the bolometer 27 and the alternating current generated thereby is passed to the amplifier 28 of matching frequency, e.g., 13 c.p.s. The amplified current is recorded at 29, on, for example, a conventional strip chart recorder in which the chart is calibrated to read current amplitudes in terms of percent water by weight of the heavy fuel oil. Alternatively, the chart may record the current amplitudes and these may be translated into percent water by weight of the heavy fuel oil by reference to a calibration table.

In cases where the heavy petroleum fuel oils contain a substanial proportion of a light hydrocarbon fuel oil, such as Navy Special Fuel Oil, the amount of hydrocarbon vapors concomitantly developed in the low pressure sample cell 10 will always be suflicient to effect complete absorption of the infrared radiation at wavelengths at which hydrocarbon vapors characteristically absorb. Thus, diminution in the signal output of the bolometer due to hydrocarbon vapor absorption of the radiation will be constant and variation in the signal output is attributed to the water content of the fuel oil.

A bandpass defining an optical interval of approximately 4-6.5 microns may be used in place of the longer interval of 1.8-9 microns. In such case, absorption of the infrared radiation due to hydrocarbon vapors is eliminated or reduced to an insignificant level.

Return flow of the water-stripped sample fuel oil to the fuel-oil supply line 11 is adjusted in accordance with the volume of the fuel oil delivered per unit of time to the sample cell 10 and is assisted by the pump 20.

In operation, the sample cell 10 of the apparatus should be located in a warm, heated area, such as near an operating boiler, to avoid condensation of water vapor in the cell and fogging of the filter windows 25 and 26, inside and out.

While the invention has been described herein with reference to certain specific embodiments thereof, these are intended by way of illustration and not in limitation except as may be defined in the appended claims.

What is claimed and desired to be secured by Letters Patent of the United States is:

1. A method of measuring the water content of a heavy petroleum fuel oil in transit in a supply line which comprises delivering said fuel oil from said supply line in heated condition into a confined low pressure zone in sample proportion and at a linear rate of flow matching that of the fuel oil in said supply line, subjecting said sample fuel oil in said low pressure zone to flash evaporation to vaporize the water content thereof, drawing said water vapor across a beam of periodically interrupted infrared radiation in said zone containing wavelengths of radiation at which water vapor characteristically absorbs, measuring the resulting absorption of infrared radifition and relating it to the water content of said heavy petroleum "fuel oil.

2. A method as defined in claim 1, wherein the sample heavy petroleum fuel oil delivered in heated condition to the confined low pressure zone is further heated in said zone to a higher temperature to ensure complete flash evaporation of the water content thereof.

3. An apparatus for measuring the water content of heavy petroleum fuel oil in transit in a supply line which comprises:

a tubular low pressure cell,

means for delivering a sample volume of said fuel oil in transit in the supply line into the lower portion of said cell and at a linear rate of flow matching that of said fuel oil in transit in said supply line,

means for flash evaporation of the water content of said sample fuel oil under low pressure in said cell, means for passing a beam of periodically interrupted infrared radiation transversely through said cell, in-

cluding wavelengths of infrared radiation at which water vapor characteristically adsorbs, means for drawing the water vapor derived from said sample fuel oil by flash evaporation under law pressure in said cell across said beam of infrared radiation in said cell, and

means for measuring the infrared radiation which has passed through said cell.

4. An apparatus as defined in claim 3, wherein the means for flash evaporation of the water content of the sample fuel oil includes a heater plate arranged in said cell for impingement thereon of the sample fuel oil entering said cell.

5. An apparatus as defined in claim 3, wherein the means for passing a beam of the periodically interrupted infrared radiation transversly through said cell includes an entrant filter window and an exit filter window mounted in the upper portion of the wall of said cell and definingthe lower and upper limits, respectively, of the pass band of said radiation.

6. Amapparatus as defined in claim 3, wherein the means for flash evaporation of the water content of the sample fuel oil and the means for drawing the water vaporsderived from the sample fuel oil across the beam of infrared radiation includes a vacuum pump and low pressure line in communication with said cell at the upper end thereof.

7. An apparatus as defined in claim 6, wherein the means for flash evaporation of the water content of the sample fuel oil includes a heater plate arranged in said cell for impingement thereon of the sample fuel oil entering said cell.

References Cited UNITED STATES PATENTS 2,835,116 5/1958 Miller 25043.5 2,918,578 12/1959 Friedman 25043.5 2,962,926 12/ 1960 Marak et al. 250-435 3,281,597 10/ 1966 Greenberg 25043.5

ARCHIE R. BORCHELT, Primary Examiner MORTON I. FROME, Assistant Examiner US. Cl. X.R. 25083.3 

